Electron emitter for electron discharge devices



July 25, 1933. v H. w. PARKER 1,919,596

ELECTRON EMITTER FOR ELECTRON DISCHARGE DEVICES Filed ec. 4, 1931 INVENTOR HEIlIH W Parker ATTORNEY Patented July 25, 1933 UNITED 'srArEs HENRY W. PARKER, 0F TORONTO, ONTARIO CANADA TUBES, LIMITED,

CANADA .FEQE

ELECTRON EMI'ITER ron Emerson nisciiAnen DEVICES Application filed December 4, 1931. Serial No. 578,930.. 7

This invention relates to electron discharge devices and pertains particularly to the cathodes of such discharge devices as are termed Braun tubes. 0

An object of this invention is to provide a cathode for electron discharge devices which will be substantially free from destructive positive ion bombardment.

A further object of this invention is to provide a cathode having a relatively long emission life.

Another object of this invention consists in providing a cathode adapted to efficiently emitelectrons from a cavity.

A still further objectcomprises providing a cavity cathode emitter which is effectively heated.

In Braun and similar tubes, especially of the type utilized now in television, the life of the tube is relatively short due to destruc tive positive ion bombardment of the cathode. Various means have been tried to overcome this defect, such as electrostatic shields arran ed in various manner to re? duce the positive ion bombardment of the cathode. Such ion bombardment unnecessarily limits the life emission of the cathode and seriously interferes with the commerclal use of such tubes. V

I have experimented With all of the known methods of reducing such positive ion bombardment 0t the'cathode and have found that none of the methods now in use reduce such bombardment in a very appreciable manner. I have been able, by the novel form of cathode emitter hereinafter described, to avoid destruction of the cathode main in the cavity Fig. 2 is an elevation of the same showing the heat retainingmember thereon; and

Fig. 3 is an elevation of the assemblv of the elements or" a Braun tube showing my;

novel emitter and its relation to other assoelated electrodes.

Referring 'nowparticularlyto Figs. 1 and '2, my novel cathode comprises a metallic tube 1, preferably of nickel, within which;

there is inserted a heatingelement composed of the refractory insulating member Q-and the heating wire 3. The inside of the other end of the tube 1 is coated with an electron emitting substance 6, I strontium oxides or combinations thereof, and this portion of the tube 1 is-separated from the heater by means ofa ceramic plug &

I p Assrenon TO noenns RADIO or- TORONTO, ONTARIO, CANADA, A cora-ro'anrron or onrARIo,

5,the function of which is to prevent light from the filament 3v 4 is electrically connected to the tube 7 1.

emerging through the open end of the tube 1. Acontact terminal 'ljhe physical principle involved is the, efii-' cient emission of electrons from a cavity.

a positiveiion travelling at enters the cavity, it will knock off active material from the inner walls of the cavity, but this active material obviously will reeven though it may be splashed to the other side. thereof. It is evident that loss of active material from the cavity is a very small probability and hence destructive action of the positive ion bombardment doesnot allow active mate rial to be lost. Preferably the. length of the coated portion ofthe tube 1 is greater than the diameter thereof. Inpractice I prefer to employ a tube having a diameter of about 0.08 of an inch andan overalllength of about 1.0 inch, thecoated portion;

being approximately four times the diameter of the tube. i

great speed c I In order to heat the active material 6, 7

it necessary to transfer sufiicient heat along the relatively thin wall of nickel tubei 1 from the heater 3 to produce a temperature great enough for breaking down the alkaline earth oxides such as strontium or barium during the activating process and later, during the operationof the cathode; for maintaining suflicient temperature for the purpose of generating evaporated electrons within the cavity. In order to effect efliciently such transfer of heat, I employ the physical principle involved in the trans' fer of heat across a multilayer of low thermal emissivity material and to that end loosely wind several layers of a very thin metallic tape 7 around the outside of the tubing to effectively thermally insulate it so that transfer of heat from the heater 3 along the length of the tubingl exists to a greater degree than would be the case if radiation perpendicularto the axis of the tube 1 were permitted. I prefer to employ a tape of thin nickel foil which is preferably highly polished, wound loosely about the tubing 1 severallayers deep and fastened at one end by spot welding to prevent ravellingf Such winding of tape very efficiently thermally insulates the tube and di rects the flow of heat along the tubing 1 at a much more rapid rate than would otherwise bethe case and at asmaller fall of thermal potential. 7

Obviously, the tube 1 could be coated or covered with a ceramic heat insulator but such coating has been found to be much less eflicient thanthe metallic tape I prefer to use and it is further difficult to degasify in the process of evacuating the tube in which the cathode is employed.

Referring now to Fig. 3, I have shown the relation of my novel cathode with respect to the usual associated anode and focusing cylinder employed in a Braun tube. The electrodes are mounted on the stem 16.

The anode disk 18 containing the aperture 19 is supported on the stem'by means of the standards 13 and 14 and the strap 15 to construction of my cathode, the emission life of the cathode is very greatly increased due to the elimination of destructive positive ion bombardment. It will be further noted that due to the novel thermal insulation of the cavity tube 1, that the transfer of heat from the heater to the emitter is efliciently effected and thus reliability of operation is increased.

Having thus completely described my invention, what I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In a cathode for electron discharge devices, a tubular heat conducting member, a heating element electrically out of contact with said member and disposed near one of the extremities thereof, a coating, of electron emissive substance disposed on the interior of said tubular member near the other extremity thereof, a ceramic plug in said member between said heater and said emissive substance and means .for effectively transferring heat from said heater along the walls of said member to said emissive substance I 2. A cathode for electron discharge devices comprising, a tubular heat conducting member, a heating elementwithin said member near one extremity thereof, a coating of electron emissive substance on the interior of said member near the other eXtremity' thereof and at least one layer of a loose spiral winding of'metallic foil on the outer surface of said member.

3. A cathode for electron discharge devices comprising, a metallic cylinder, a heating element within said cylinder near one extremity thereof, a coating of electron emitting substance on the interior of said cylinder near the other extremity thereof, and 1 1105 a winding of metallic foil on the outside of said cylinder.

4. A cathode for electron discharge devices comprising, a metallic cylinder, a heating element within said cylinder near one extremity thereof, a coating of electron emitting substance 011 the interior of said cylinder near the other extremity thereof, a ceramic plug in said cylinder between said emitting substance and said heater and awinding of. metallic foil on the outside of said cylinder.

' HENRY W. PARKER. 

